Electron discharge device



L E u M A 5 lm A ELECTRON DISCHARGE DEVICE Filed Oct. 28. 1941 FIG. 2

L M MA VS mWL m A m w 3 6. A 2 a O 8. A O B 6 M 2 0 8 6 4 d 6 MunATTORNEY Patented May 4, 143

ELEGTRON DISCHARGE DEVICE Application Gctober 28, 1941, Serial No.416,785

7 illaims. .(Cl. 250-27) This invention relates to electron dischargedevices and more particularly to such devices of the electron beam andvirtual cathode types.

One general object of this invention is to improve the operatingcharacteristics and efficiency of electron beam discharge devices. Morespecifically, objects of this invention are to:

Expedite the attainment of high current density electron beams inelectron discharge devices;

Facilitate the production of a virtual cathode in electron dischargedevices; 7

Improve the operating stability of devices of the virtual cathode type;7

Increase the transconductance of electron discharge devices; and

Reduce the conduction current to the control electrode or grid in suchdevices.

In one illustrative embodiment of this invention, an electron dischargedevice comprises an anode or target electrode, an electron gun forprojecting an electron beam toward the target electrode, and anelectrode system between the electron gun and the target electrode oranode.

In accordance with one feature of this invention, the electrode systemcomprises a pair of spaced, aligned, centrally apertured electrodemembers so constructed and arranged and related to the electron gun thatin the region between the two members the electrons in the beam aredirected along parallel paths, and when the electrodes are energized apotential zero is established immediately adjacent the electrode memberfurthest removed from the electron gun whereby a virtual cathode isproduced immediately adjacent the aperture in this electrode member.

In accordance with another feature of this invention, a controlelectrode or grid is mounted within or in the immediate vicinity of theaperture in the electrode member furthest removed from the electron gun,this electrode or grid being effective to vary greatly the currenttransmitted through this aperture, in accordance with relatively smallchanges in its potential.

In accordance with a further feature of this invention, the controlelectrode is a wire frame or ring in close proximity to the boundary ofthe aperture mentioned whereby, when this electrode is positive andelectron current is transmitted through the aperture, the electrode iseffective to increase the focussing of the beam and thus the conductioncurrent to this electrode is very small.

The invention and the above-noted and other features thereof will beunderstood more clearly and fully from the following detaileddescription with reference to the accompanying drawing in which:

Fig. 1 is a diagrammatic view of an electron discharge deviceillustrative of one embodiment of this invention; and

Fig. 2 is a graph illustrating appropriate forms of the electrodemembers in the device shown in Fig. 1.

Referring now to the drawing, the electron discharge device illustratedin Fig. 1 comprises an evacuated enclosing vessel to, shown in phantom,within which there are mounted an anode or target electrode H and anelectron gun for producing a concentrated sheet-like electron streamwhich is projected toward the anode or target electrode H. The electrongun, which may be of the construction disclosed in the applicationSerial No. 307,233, filed December 2, 1939, of John R. Pierce, comprisesa cathode I2 having a dished electron emissive surface L3 and a pair ofaligned, centrally apertured beam formthe electrodes l4 and I5, theelectrode I extending from adjacent the periphery of the emissivesurface i3 and the electrode l5 being dished toward the cathode. Asshown, the cathode may be of equipotential type and comprise a heaterfilament It. The electrode I l may be connected to the cathode, forexample, directly by a conductor ll, the cathode may be at groundpotential, and the electrode l5 may be maintained at a positivepotential with respect to the cathode 16 by a suitable source, such as abattery [8.

Mounted between the electron gun and the anode or target electrode IIand in alignment therewith are a pair of centrally apertured electrodesHand 20. The electrode 19 may be integral with the electrode #5 asshown, so that it is maintained at the same potential as the electrodel5, and the electrode 20 may be operated at cathode potential, beingconnected to the cath ode, for example, by a conductor 30.

A control electrode or grid is mounted within the aperture in theelectrode 20 and, in one form, includes'a wire frame 2| and a grid orreticulated portion 22. The control grid is biased at a negativepotential with respect to the cathode, as by a battery 23, and itspotential may be varied in accordance with a siignal impressed acrossthe input resistor 24.

The anode or target electrode II is operated at a positive potentialwith respect to the oathode, as by a battery 25 in series with theoutput resistor 26.

The electrons emanating from the emissive surface-l3 areconcentratedinto a converging cated by the broken lines B, which isprojected through and substantially fills the aperture in the electrode[5, traverses the region between the electrodes I and I9 and emergesfrom the aperture in the latter electrode. The apertures in theelectrodes l5 and I9 are made such, in accordance with known principles,that the lens actions thereof result in parallel electron flow, parallelto the axis of alignment of the electrodes, at the aperture in theelectrode Hence, at the region of entry of the electrons into the spacebetween the electrodes I9 and 20, the electron flow is parallel to theaxis of align: ment of the electrodes.

The electrodes I 9 and 20 are so constructed and arranged that in theregion therebetween the electrons are directed along parallel pathsbetween boundaries passing immediately adjacent the edges of theelectrode 20 bounding the aperture therein. The principles involved insuch construction and arrangement are set forth fully in the applicationSerial No. 416,778, filed October 28, 1941, of John R. Pierce. It willbe noted, however, that the electrodes I9, 20 and Il constitute anelectrode system wherein the end electrodes I9 and II are at positivepotentials and in which the potential distribution is such that apotential zero exists at the plane of the aperture in the electrode 26.The electrodes I9 and 2|, then, are of the form given by the relationwhere u and v are the rectangular coordinates of each electrode, 1)being taken normal to the electron fiow and equal to zero at the beamboundary, i is a constant proportional to the potential of the electrodei= /-1, and I is a complementary function. Several appropriateconfigurations of the electrodes I9 and 20 for various values of I areshown in Fig. 2.

The electrons emanating from the aperture in the electrode I9 flow alongparallel paths toward the aperture in the electrode 20. When the controlgrid 2|, 22 is at a negative potential, all of the electrons come torest momentarily adjacent the control grid, whereby a virtual cathode isestablished, and are reflected toward the electrode I 9. However, whenthe control grid becomes positive, as in accordance with an input signalimpressed across the resistor 24, the electrons, in number determined bythe'potential of the control grid, will pass through the control gridand flow to the target electrode or anode I I.

It will be appreciated that the electrodes I5 and I9 may be operated athigh positive potentials with respect to the cathode I2 so that largecurrents may be drawn from the cathode and a virtual cathode of highcurrent capacity thus realized in the immediate vicinity of the controlgrid. It will be noted also that the electrons transmitted through thecontrol grid leave the region thereof with low velocities so thatdivergence of the electron stream due to space charge effects, is smallin the region between the control grid and the anode or targetelectrodes.

Furthermore, it will be appreciated that the control grid is mounted inimmediate proximity to the region at which the virtual cathode isestablished so that highly sensitive control of the transmitted currentand high transconductances are obtained. Moreover, because of theconstrainment of the electrons to parallel flow in the region betweenthe electrodes I9 and 20, stable operation of the device is achieved.

sheet beam, the boundaries of which are indi- Although the controlelectrode has been described as comprising a grid or reticulated portion22, it may very advantageously consist of the wire frame ZI. In suchcase, as in the construction described hereinabove, when the electrode2| is at a negative potential all of the electrons projected from theaperture in the electrode I9 will be reflected. However, when theelectrode 2! becomes positive, the transmitted electrons are highlyconcentrated and focused to pass through the aperture bounded by thewire frame electrode 2| so that the current to this electrode isextremely small.

Although in the particular embodiment shown and described the currenttransmitted through the control electrode flows directly to the targetelectrode I I, the invention may be embodied also in devices wherein thetransmitted current is acted upon in various ways between the controland target electrodes. For example, suitable electrodes for velocityvarying this current may be provided between the control and targetelectrodes and appropriate means also provided for extracting energyfrom the electron stream after it has been velocity varied.

Also, although the invention has been described with particularreference to devices utilizing a sheet-like electron beam and whereinthe electrodes are symmetrical with respect to the longitudinal medialplane of the beam, it may be embodied also in devices utilizing acylindrical beam and wherein the electrodes are axially symmetrical. Inthis case, the electron gun may be of the construction described in theapplication Serial No. 319,393, filed February 17, 1940, of John R.Pierce, and the requisite forms for the electrodes I9 and 2!] determinedby the use of an electrolytic tank as described therein.

It will be understood, of course, that various modifications may be madein the specific embodiment shown and described without departing fromthe scope and spirit of this invention as defined in the appendedclaims.

What is claimed is:

1. Electron discharge apparatus comprising a target electrode, anelectron gun for projecting an electron stream toward said targetelectrode, a control electrode intermediate said electron gun and saidtarget electrode, and means for directing the electrons in said streamalong parallel paths throughout a region between said gun and saidcontrol electrode and extending to immediately adjacent said controlelectrode gun, said means including a pair of aligned electrodes one ofwhich is mounted between said gun and said control electrode and theother of which extends outwardly from immediately adjacent said controlelectrode. 7

2. Electron discharge apparatus comprising a target electrode, meansincluding a cathode for projecting a stream of electrons toward saidtarget electrode, a control electrode intermediate said means and saidtarget electrode, and means for establishing a region of zero potentialimmediately adjacent said control electrode, said last means including apair of centrally apertured electrodes intermediate said cathode andsaid target electrode and in alignment with said cath ode, one of saidapertured electrodes being connected electrically to said cathode andextending outwardly from immediately adjacent the periphery of saidcontrol electrode and the other of said apertured electrodes beingmounted intermediate said cathode and said control electrode and adaptedto be maintained at a positive potential relative to said cathode.

3. Electron discharge apparatus comprising a target electrode, means forprojecting an electron stream toward said target electrode including acathode and an accelerating anode, a control electrode intermediate saidmeans and said target electrode, and means for producing a virtualcathode immediately adjacent said control electrode, said last meansincluding said cathode and a pair of electrodes one of which is mountedadjacent said accelerating electrode and electrically integral therewithand the other of which is mounted immediately adjacent said controlelectrode and is electrically connected to said cathode.

4. Electron discharge apparatus in accordance with claim 1 wherein saidcontrol electrode consists of an electrically conductive frame.

5. Electron discharge apparatus comprising a pair of aligned, centrallyapertured electrodes, the opposed surfaces of said electrodes beingdished in the same direction, an electron gun opposite one of saidelectrodes and aligned therewith, a target electrode opposite the otherof said electrodes, and a control electrode mounted within the aperturein said other electrode.

6. Electron discharge apparatus in accordance with claim 5 wherein saidelectron gun comprises a cathode and an accelerating anode and whereinsaid one electrode is connected electrically to said anode and saidother electrode is connected electrically to said cathode.

7. Electron discharge apparatus comprising an electron gun including acathode and an accelerating electrode in cooperative relation with saidcathode, a target electrode spaced from said gun, a control electrodeintermediate said electron gun and said target electrode and inalignment with said gun, and means for confining the electrons emanatingfrom said gun to parallel paths throughout a region extending fromimmediately adjacent said control electrode toward said gun, said meanscomprising a pair of centrally apertured electrodes in alignment withsaid gun, one of said apertured electrodes extending outwardly fromimmediately adjacent said control electrode and being electricallyconnected to said cathode and the other of said apertured electrodesbeing mounted intermediate said accelerating and control electrodes.

ARTHUR L. SAMUEL.

